SAN BRUNO — Pacific Gas & Electric lost electric power to a key part of its natural gas pipeline system at its control center in Milpitas only hours before an explosion ripped through a San Bruno neighborhood, killing seven and destroying 37 houses.

The new information was made public Monday by U.S. Rep. Jackie Speier, D-Hillsborough, at a news conference to unveil a new piece of pipeline safety legislation.

“I think we will probably find out months later that it was a perfect storm,” Speier said. “It was a number of factors that came together to create an environment in which the explosion took place. There is also an issue about the loss of electricity that occurred earlier in the day and the bringing the system back up and whether or not everything was synchronized properly.”

Speier did not elaborate, but Peter Knudson, a spokesman for the National Transportation Safety Board in Washington, confirmed that equipment known as the uninterruptable power supply system, at the Milpitas control center, shut down. The line that exploded, Line 132, originated in Milpitas and ran north to San Francisco.

PG&E crews had been working on the power supply system, Knudson said.

“We are looking at whether it played a role in the accident,” he said.

Two weeks ago, Christopher Hart, vice chairman of the NTSB, told the Mercury News in an interview that federal investigators went to the Milpitas control center, located near Interstate 880 and Highway 237, on Sept. 14, and copied records from its computer system and pipeline pressure sensors, equipment Hart described as “loosely analogous to the black box in an airplane.”

A loss of electrical power could have affected the computer system and other equipment that monitors and maintains natural gas pressure in the pipe. Last week, the Mercury News reported that pressure in the line was 386 pounds per square inch, higher than the 375 psi that PG&E says was its limit, but still below the “maximum allowable operating pressure” of 400 psi that the pipe was rated for.

The development came on the same day Speier announced legislation that would require pipeline operators across the country to equip their lines with automatic shut-off valves, a technology that could have significantly reduced the devastation of the lethal San Bruno pipeline explosion.

The bill also would require pipeline operators to tell homeowners whether they live near high-pressure gas mains.

Speier unveiled the legislation, which is to be introduced today,﻿ while standing in front of the crater left by the explosion.

“We have an aging natural gas pipeline running through our communities,” said Speier, flanked by San Bruno’s police and fire chiefs as well as the vice mayor. “Are the lines too old; are they safe?” California Sens. Dianne Feinstein and Barbara Boxer have introduced a similar bill in the U.S. Senate.

Following the explosion earlier this month, PG&E workers had to manually shut off the flow of gas to the 30-inch transmission line, a process the utility has said took an hour and 46 minutes. PG&E workers turned cranks by hand on the valves, one of which was located under a manhole and the other in a locked building, each roughly a mile from the explosion site.

San Bruno and Millbrae Fire Chief Dennis Haag said Monday that stopping the flow of gas earlier would have reduced the amount of damage from the searing heat.

“Without that fuel source, we could have made an offensive attack much sooner that we did,” Haag said. “We were in defensive mode until the shut-off was completed.”

PG&E officials told Speier’s staff Monday that there are 20 manual valves on Line 132, which runs from Milpitas to San Francisco. It can cost up to $250,000 to install an automatic shut-off valve on an existing line. An automatic shut-off valve closes when gas pressure changes significantly.

A PG&E spokesman said Monday that the company already has hundreds of automatic shut-off valves in its pipelines, and PG&E officials told Speier’s staff that there are nine on its gas mains in San Francisco and San Mateo counties. He added that the utility has replaced some manual valves with automatic ones.

A similar type of valve, known as a remote shut-off valve, can be closed by an operator pushing a button miles away. It was not clear Monday how many automatic and remote valves are located in other Bay Area counties.

“We continue to meet with government officials, and we share their desire to find ways tragedies such as this one can be prevented in the future,” PG&E spokesman Matt Nauman said. “As we all look for answers about whether or not this could have been prevented, we do want to share our learnings with other pipeline operators.”

If Speier’s bill becomes law, within two years utilities would have to notify people who live within 2,000 feet of a gas transmission line of the location of that line. The companies also would be required to install automatic or remote shut-off valves on all new natural gas transmission pipelines, and within two years on all pipelines within 10 miles of a high-risk earthquake fault, like the San Andreas or Hayward faults. Within five years, such valves would be required on natural gas transmission lines in all highly populated areas.

Under the legislation, utilities also would have to internally inspect their pipelines, using devices that are known in the industry as “smart pigs.” The companies would have to do the inspections every five years, and, according to Speier’s bill, “if that is not possible, they are prohibited from operating the pipeline at high pressure.”

Because the line in San Bruno is of different sizes and contains some bends, that type of inspection was not possible. Speier said the line that blew up should be removed from the neighborhood.

Speier said she looks forward to working with Feinstein and Boxer, whose legislation would double the number of federal pipeline inspectors, bump up the penalties for pipeline safety violations and require automatic shut-off valves. However, Speier said the Senate bill requires the valves only if they are “economically and technologically feasible.”

“I don’t think economics should play a role in this any longer,” she added.

The bill may encounter opposition from the oil, gas and pipeline industries in Congress.

In testimony Thursday before the House Commerce Committee, Andrew Black, president of the Association of Oil Pipelines, said pipelines are the safest way to transport hazardous liquids and that lawmakers shouldn’t rush to write new rules.

“We believe Congress should think carefully about the consequences of overhauling a regulatory model that is driving down the number of releases and incidents from pipelines,” Black said, adding that the cause of the San Bruno explosion hasn’t yet been determined.